Method and device for improving the external ballistics of an artillery shell

ABSTRACT

The present invention relates to a method and a device for improving—at least in part—the external ballistics of primarily the type of artillery shells ( 1 ) that are fin-stabilised in their trajectory towards the target and thus have a slipping plastic driving band ( 6 ) which, during firing of the said shell from a designated barrel, constitutes the shell&#39;s direct contact with the inside of the barrel. The problem that it is the function of the present invention to resolve is that the slipping plastic driving band ( 6 ) normally detaches immediately outside the muzzle of the barrel used for firing, thereby leaving an open groove ( 4 ) that causes distrubing turbulence which is detrimental to the flight of the said shell. The solution to the problem herein proposed is based on a ring-shaped spring-loaded device ( 5 ) arranged between the driving band ( 6 ) and the bottom of the driving band groove ( 4 ) and which device is held pressed against the bottom of the said driving band groove as long as the driving band ( 6 ) is in position but as soon as it detaches from the said driving band groove the said device deploys to re-assume a pre-determined original shape which completely fills the driving band groove ( 4 ) up to and level with the outer surface of the shell ( 1 ).

[0001] The present invention relates to a method and a device for improving—at least in part—the external ballistics of primarily the type of artillery shells that are fin-stabilised in their trajectory towards the target and thus have a slipping plastic driving band which, during firing from a designated barrel, constitutes the shell's direct contact with the inside of the barrel.

[0002] The slipping plastic driving band means that this type of shell exits the barrel with a very low rate of spin or no spin at all, which obviously facilitates the fin stabilisation of the shell which shall be effected immediately it exits the muzzle by means of deployment of a plurality of fins previously retracted and integrated in the shell. The plastic driving band is usually so worn out from its severe treatment during the shell's passage through the barrel that the remnants of the driving band break away from their seat around the shell as the shell exits the muzzle of the gun in which it is fired. As soon as the shell has left the muzzle the well-defined groove in which the slipping plastic driving band was originally seated thus becomes revealed in the otherwise smooth external surface close to the rear face of the shell.

[0003] No one has previously paid any attention to the empty driving band groove, but now when every means available is being employed in attempts to increase the range of tube-firing artillery it has been ascertained that the empty, sharply-defined driving band groove causes turbulence in the surrounding atmosphere that cannot be ignored as it has a retarding, disturbing effect on the shell during its trajectory to the target.

[0004] The objective of the present invention is to resolve this problem by offering a method and a device which, without interfering with the functioning of the slipping driving band, fills the driving band groove as soon as the remnants of the driving band have detached from the said groove, thus enabling elimination of the otherwise disturbing turbulence around the driving band groove in an effective way.

[0005] The fundamental principle for the method as claimed in the present invention is an arrangement between the bottom of the driving band groove and the slipping driving band incorporating a ring-shaped, spring-loaded device that is initially compressed and which, as long as the driving band is in position, is held pressed against the bottom of the driving band groove by the driving band but which device, as soon as the driving band or remnants of the driving band have detached from the driving band groove, deploys and re-assumes a predetermined original shape that completely fills the driving band groove to be level with the outer surface of the shell.

[0006] This fundamental principle provides space for a device comprising an open first part made of a springback material and arranged in the driving band groove, and which first part is the same width as the said groove and has a length equivalent to the circumference of the shell at a position level with the driving band groove and when in deployed state forms a circular ring with an open gap between its two ends and comprises a plurality of identical filler elements made similarly of springback material mounted in the said first part and directed in deployed state at the bottom of the driving band groove, which filler elements are so designed that they can be pressed in against the inside of the said first part at the same time as the first part can be retracted against the bottom of the driving band groove with the ends of the said first part overlapping while allowing space outside the said first part in the driving band groove for the actual driving band.

[0007] According to a preferred variant of the present invention the filler elements are designed such that in deployed state they extend from each attachment point in the said first part in a slight arc in towards the bottom of the driving band groove, which they reach in a mainly tangential direction. This variant provides good centring of the first device so that in deployed state it gives a precise filling out of the driving band groove.

[0008] If all the filler elements are also given such a length and are attached to the inside of the said first device with such a distance between the attachment points that there is adequate space to accommodate them between each other when the said device is retracted around the bottom of the driving band groove one achieves a filler device which, when in retracted state, has a thickness that in principle is only equivalent to double the thickness of the material of which the first ring-shaped device and filler elements are fabricated, and for this purpose it is appropriate to use a titanium-based sheet metal with good shape memory.

[0009] Finally, it can also be noted that the combined latent spring force, when the first part of the device is retracted around the bottom of the driving band groove and its filler elements are retracted against the said first part, does not need to be greater than that the said first part is held in place by the driving band arranged on top as long as the latter has not come into use.

[0010] The present invention is defined in the subsequent Patent Claims, and is now described in only slightly more detail with reference to some relevant figures.

[0011] In these figures

[0012]FIG. 1 depicts an oblique projection of a fin-stabilised shell equipped with a filling, as claimed in the present invention, of the shell's driving band groove after detachment of the slipping driving band, and

[0013]FIG. 2 is a section through the shell at a position level with the driving band groove with half the driving band illustrated in its original position, while

[0014]FIG. 3 depicts the same section as FIG. 2 but with the driving band groove filler as claimed in the present invention fully deployed.

[0015] The shell 1 depicted in FIG. 1 is fin-stabilised with six aft fins 2 and is guided in its trajectory by four canards 3. Near the deployed aft fins there is a driving band groove 4 which, in the mode illustrated in FIG. 1, is filled by the device 5 claimed in the present invention.

[0016]FIG. 2 shows a section through the shell 1 level with the driving band groove 4, in part of which a driving band 6 is illustrated. There is a driving band groove filler 5 compressed under the driving band 6 against the bottom of the driving band groove 4. FIG. 3 depicts the driving band groove filler 5 in deployed state in which it completely fills the driving band groove after the driving band has detached from the groove. As shown in FIG. 3 the driving band groove filler 5 consists of an outer ring 7 of springback material of the same width as the driving band groove and with preferably at least the same length as the circumference of the shell 1 at a position level with the driving band groove 4. A plurality of springback filler elements 8 are arranged inside the outer ring 7. When deployed the said elements extend in a slight arc from each of their attachment points down to a tangency of the bottom of the driving band groove 4 herein designated 9. The distance 11 between the attachment point in the outer ring 7 of each filler element 8 and the attachment point of the next filler element is such that the length of each filler element in compressed state has adequate space between its own attachment point and the attachment point of the next filler element. The design of the filler elements 8 is such that the outer ring 7 in deployed state is supported concentrically around the bottom of the driving band groove 9 precisely level with the outer surface of the shell where the outer ring 7 forms a continuation that spans the full width of the driving band groove. As shown in FIG. 3 the outer ring 7 is somewhat shorter than the fill circumference of the shell, while a bridging element 12 attached to one end of the said outer ring covers the gap between the opposite ends of the said outer ring. The gap between the said ends is equal to the difference between the circumference of the shell and the circumference around the bottom of the driving band groove. 

We hereby claim and desire to secure by Letters Patent the following:
 1. A method for artillery shells (1), of the type equipped with a slipping driving band (6) that constitutes the shell's direct contact with the inside of the barrel from which it is fired and which driving band is arranged in a designated driving band groove (4), of eliminating the risk that the driving band groove (4) in which the slipping driving band (6) is initially fitted should give rise to disturbing turbulence during the flight of the shell (1) to the target after the remnants of the driving band (6) have detached from the said driving band groove outside the muzzle of the barrel wherein a ring-shaped spring-loaded device (5) is initially arranged between the driving band (6) and the bottom of the driving band groove (4) and which device as long as the said driving band is in position is held by the latter pressed against the bottom of the said driving band groove, but as soon as the said driving band has detached from its said groove the said device deploys and re-assumes a previously determined original shape that completely fills the said driving band groove up to and level with the outer surface of the shell (1).
 2. A device for the method claimed in claim 1 for such artillery shells (1) that have a slipping driving band (6), which constitutes the shell's direct contact with the inside of the barrel from which it is fired, arranged in a designated driving band groove (4), whereby in the event that the said driving band detaches from the said driving band groove outside the muzzle of the barrel the claimed device eliminates any risk that the driving band groove (4), after the shell (1) has left the muzzle, should give rise to disturbing turbulence in the adjacent atmosphere during the flight of the shell to the target, wherein the said device comprises an open first part (5) made of a springback material and arranged in the driving band groove (4), and which first part has the same width as the said driving band groove and a length equivalent to the circumference of the said shell at a position level with the driving band groove (4), and which first part in deployed state forms a circular ring with an open gap between both ends of the said first part together with a plurality of identical filler elements (8) made of the same type of springback material as the said first part to which they are attached, and which filler elements when deployed are directed at the bottom of the said driving band groove, and which filler elements are so designed that they can be pressed in against the inside of the said first part at the same time as the said first part can be retracted around the bottom of the said driving band groove with the ends of the said first part overlapping each other while still allowing space in the said driving band groove for accommodation of the said driving band.
 3. A device as claimed in claim 2 wherein the filler elements (8), which are secured in the said first part and face the bottom of the said driving band groove, in deployed state extend from each attachment point in the said first part in a slight arc in towards the bottom of the driving band groove (4) which they reach in a mainly tangential direction.
 4. A device as claimed in claim 3 wherein each filler element (8) has been given such a length and has been attached to the inside of the said first part (5) at such a distance between the attachment points that when the said device is retracted around the bottom of the said driving band groove the said filler elements have adequate space between each other without overlap.
 5. A device as claimed in any of claims 2-4 wherein the combined latent spring force, when the said first part is retracted around the bottom of the said driving band groove and its filler elements (8) are retracted against the said first part, is no greater than that the said first part is held in place by the driving band (6) arranged on top as long as the latter has not come into use. 